Household waste comprises a smaller or larger part of organic waste which can be processed by digestion. For this purpose the non-digestible parts such as metal, sand and glass, stone, plastic bottles and foil must first be removed. Many separating methods are known for this purpose, including shredding, pressing and screening. The remaining, substantially organic material can then be further comminuted. Cell walls will break here and a pasty material results comprising moisture and solid organic material. In addition to particles of pasty organic material, pieces of plastic foil which have not been removed from the waste during the preceding process steps, for instance because they have been able to pass through screen openings, will however usually also be present in the comminuted material. It is important to also remove these pieces of plastic foil before admitting the comminuted material into a digester since they can disrupt the digesting process.
Many methods and devices are known for mutually separating particles of different size, weight, mass density and/or shape. Use can thus be made here of gravitational force, mass inertia or centrifugal forces. Examples hereof can be found in patent documents classified within B01D (IPC). Use can also be made of a centrifuge comprising a drum or rotor. Examples hereof can be found within B04B (IPC). Also known is a cyclone: a device in which a more or less free vortex or swirling is created. Examples hereof can be found within B04C (IPC). It is further known to screen and divide particles according to size, by means of screens, grids and the like, or according to weight and/or size by means of gas or airflows, wherein gravitational force and/or air resistance play a part. Examples hereof can be found in patent documents classified within B07B (IPC).
US20090230224A1 thus describes a system for ‘separating glass and plastic foils in laminated glass’. Use is made here of a drum with a rotor rotating therein provided with beaters with which the glass is broken into pieces. The heavier glass particles then fall downward and through perforations arranged in the underside of the drum. The lighter foil particles are carried along by an airflow generated by blades arranged on the rotor. Such a system is found to be unsuitable for separating pieces of plastic foil and particles of pasty organic material because an effective and sufficient separation thereof is not possible on the basis of gravitational force and air resistance. The perforations will also quickly become clogged and the yield will be minimal. JP2002177888A describes a device for separating foreign matter from organic waste. Use is made here of a drum which is provided on the underside with perforations, and a rotor rotating in the drum and provided with vanes which slide along the inner side of the drum. Following introduction of the waste into the drum the waste is shredded and comminuted. The organic material drops to the underside of the drum and leaves the drum through the perforations there, assisted here by the vanes. Foreign materials are further carried away by an airflow. This system is also found to be unsuitable for separating pieces of plastic foil and particles of pasty organic material because an effective and sufficient separation thereof is not possible on the basis of gravitational force and air resistance. Here too the perforations will also become quickly clogged and the yield will be minimal.
Many other systems for mutually separating particles of different size, weight, mass density and/or shape are thus known. None of these known systems is however found to be suitable in practice for effective and sufficient mutual separation of said pieces of plastic foil and particles of pasty organic material. There is therefore a need for a solution here. The present invention now provides this.